Most people barely glance at their fingernails, but your nails are far more than a cosmetic feature — they’re small diagnostic windows into your overall health. In fact, hundreds of medical conditions can create visible nail changes. While many issues come from harmless causes like aging, fungal infections, or minor trauma, some nail signs can point to deeper health problems involving the liver, heart, thyroid, or lungs.

Understanding these clues can help you catch imbalances early and know when to seek medical advice.

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The “Half Moons” at the Base of the Nails

A healthy nail typically appears pink with a light pink-to-white crescent at the base, called the lunula. According to Dr. L. Reed, ND, these half-moons may correlate with thyroid function. Missing lunulae on multiple fingers can indicate potential thyroid weakness, which may relate to symptoms like fatigue, thinning hair, mood swings, or depression.

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Texture, Color & Shape: What’s Normal?

Healthy nails should be smooth and even — without ridges, spots, grooves, or discoloration. When the appearance changes for no clear reason, your body may be trying to get your attention.

Below are the most important signs to examine.

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1. Brittle or Crumbly Nails

Common causes:
• Aging
• Frequent exposure to detergents or nail polish

Possible medical causes:
• Fungal infections
• Lichen planus
• Thyroid disorder
• Psoriasis
• Rarely: reactive arthritis

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2. Discolored Nails

Yellow

May be caused by nail polish, but can also indicate:
• Fungal infection
• Psoriasis
• Liver issues (jaundice)
• Sinus infection
• Thyroid issues
• Lung infection
• Lymphedema

Green–black

Usually due to a bacterial infection beneath a loose nail.

Blue or purple

May indicate low oxygen levels.

Grey

Can result from certain medications.

Brown

May signal thyroid disease or malnutrition.
Half-white at the base and half-brown at the tip can indicate:
• Kidney failure
• AIDS
• Post-chemotherapy changes

White nails

Possible causes:
• Aging
• Fungal infections
• Iron deficiency (anemia)
• Liver cirrhosis
• Heart or kidney failure
• Diabetes
• Hyperthyroidism
• Malnutrition
• Chemotherapy

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3. Thickened Nails

Most often due to fungal infections, but can also indicate:
• Psoriasis
• Reactive arthritis
• Lung disease (yellow, thick, slow-growing nails)

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4. Loose Nails (Onycholysis)

Nails that lift from the nail bed may result from:
• Injury
• Infection
• Thyroid disorder
• Psoriasis
• Poor circulation
• Medication reactions

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5. Spoon-Shaped Nails (Koilonychia)

Nails curve inward like a spoon. May signal:
• Iron deficiency
• Hemochromatosis (iron overload)
• Raynaud’s disease
• Heart disease
• Hypothyroidism

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6. Pitting or Dents

Small indents can be associated with:
• Psoriasis
• Eczema
• Alopecia areata
• Reactive arthritis

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7. Beau’s Lines (Deep Horizontal Grooves)

Possible causes include:
• Chemotherapy
• Previous trauma
• Severe cold exposure
• Raynaud’s syndrome
• Diabetes
• Vascular disease
• Zinc deficiency
• High fever illnesses

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8. Nail Clubbing

Nails curve around enlarged fingertips.
While sometimes hereditary, sudden clubbing can signal:
• Chronic lung disease
• Heart disease
• Liver disease
• Inflammatory bowel disease
• AIDS

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9. White Lines Across the Nails (Muehrcke’s Lines)

Run parallel to the nail base.
May indicate low protein levels due to:
• Malnutrition
• Liver disease

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10. Dark Vertical Stripes

Common and harmless in many people with darker skin tones.
However, if affecting one nail only, it may indicate:
• Subungual melanoma (a rare skin cancer)

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11. Red or Brown Streaks Under the Nails

Called “splinter hemorrhages.”
Usually from tiny blood vessel damage — harmless unless affecting many nails, which may suggest an underlying condition needing evaluation.

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Final Thoughts

Your nails are constantly recording your internal health. While most abnormalities are harmless, persistent or unusual changes deserve attention. Checking your nails regularly helps you spot early clues and take action long before major symptoms appear.